feat(ui): add audio player component, presign API route, and reading progress tracking

ui/src/routes/api/progress/+server.ts

@@ -0,0 +1,19 @@
+import { json, error } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { setProgress } from '$lib/server/pocketbase';
+
+/**
+ * POST /api/progress
+ * Body: { slug: string, chapter: number }
+ * Records the user's reading position for the current session.
+ */
+export const POST: RequestHandler = async ({ request, locals }) => {
+	const body = await request.json().catch(() => null);
+
+	if (!body || typeof body.slug !== 'string' || typeof body.chapter !== 'number') {
+		error(400, 'Invalid body — expected { slug, chapter }');
+	}
+
+	await setProgress(locals.sessionId, body.slug, body.chapter);
+	return json({ ok: true });
+};